40 db compared to 20 db is -

SPL = Sound pressure level If a sound has an SPL of 1000 i.e (103) times, the reference of sound, it is expressed as 20 × log 1000 = 20 × 3 = 60 dB (as log 1000 = 3) Now in the Q sound is 20 dB, that means to get 20 as the answer, 20 has to be multiplied by 1, i.e the SPL of this sound is 10 (because log 10 is 1). Now it is being compared with 40 dB To get 40 dB as the answer. 20 has to be multiplied by 2 which means log of x = 2, therefore x = 100 So it means this sound should have SPL = 100 Now see = 20 dB = SPL 10 40 dB = SPL 100 i.e. 40 dB is 10 times of 20 dB